This invention relates to systems for monitoring processes where an intense point source of light is generated incident to a metal working process, and is specifically concerned with a video monitoring system and method for monitoring a gas and arc welding or cutting operation.
Systems for video monitoring an arc welding operation are known in the prior art. Such systems are often used in situations where it is impossible or impractical for a human operator to have direct, hands-on access to the workpiece such as when a weld must be produced in the inner diameter of a pipe, or within the radioactive environment of a nuclear steam generator. These video monitoring systems allow the welder to observe the position of the electrode and the filler wire relative to the workpiece, as well as the characteristics of the weld puddle created by the electric arc. This information helps the operator to remotely control the dynamics of the weld puddle so that the weld is produced uniformly and without flaws.
Unfortunately, the images produced by such video monitoring systems are generally not as clear and informative to a welder as the image he might see through a conventional welding hood. This difference in quality stems largely from the fact that the sensing circuit of a conventional television camera (which is a pixel array of a light-sensitive charge coupled device) does not have the interpretative abilities that the human eye does when used in combination with the brain. While the filter glass used in a conventional welding hood produces an image wherein the arc is essentially white and the background of the workpiece is very nearly black, the eye and brain are able to interpret this image so that the welder is able to see fairly clearly the position of the electrode of the torch relative to the workpiece, the resulting weld puddle, the contour of the weld, and the wettability of the leading edge of the puddle. However, in the case of a television camera, the bright image of the arc saturates a portion of the charge coupled device (CCD) of the light sensing circuit, yielding a television image that includes severe contrasts wherein the background surrounding the electric arc is darkened into obscurity. Additionally, the applicant has noted that some of the light filtration components in these systems are apt to create "ghost" images and stray refractions which further blur the resulting image. In an attempt to balance these severe contrasts, some prior art television systems have employed pulsed light sources such as xenon flash units or lasers synchronized with the actuation of the television camera, in combination with narrow bandwith filters which conduct only a very narrow range of light frequencies that are present in the spectrum of the arc light. Unfortunately, the use of such background lighting necessitates the positioning of still another component in the often limited access area around the weld, and significantly increases the cost of the operation of the monitoring system. Additionally, systems that use such narrow bandwidth filters are only capable of generating a black and white image, which gives the system operator less information than a color image, particularly when the system is used to inspect a completed weld.
In addition to the problem of obscuring contrasts, a second major problem associated with many prior art systems is the mechanical interference that the components of the video monitoring system impose upon the movement of the weld head. In some systems, the movement of the weld head is limited by a relatively large and bulky camera assembly which is connected directly on the weld head. The relatively large and bulky size of such camera assembly is due in part to the fact that such assemblies must contain not only the television camera, but a separate array of lenses, electronic light valves, iris diaphragms, neutral density filters or cross-polarizing filters all positioned in tandem which are used to dim the image of the arc before it strikes the light-sensitive array of charge coupled devices within the camera. In an attempt to solve the mechanical interference problems caused by the mounting of the camera assembly on the weld head, some other prior art systems use fiber optical cables to remotely transmit an optical image to a television camera. However, these fiber optical cables lose a great deal of the transmitted light which reduces the resulting resolution of the television image, and are easily browned and burned out by radiation which in turn necessitates frequent replacement.
Clearly, there is a need for a television monitoring system for observing a welding operation which produces a clear, sharp and contrast-balanced image where the portion of the workpiece surrounding the welding arc is easily visible without the need for auxiliary background lighting. Ideally, such a system should be compact enough in design so as to offer little or no mechanical interference to the weld head as it is manipulated during a welding operation. Moreover, the system should be comprised of a small number of simple and inexpensive parts that are capable of producing a clear and well lighted welding images under a variety of different conditions and for a variety of different welding systems. Finally, the system should be sensitive to a variety of different light frequencies so that the generation of a color image is possible, be easily installable onto a variety of existing tungsten-inert gas weld heads, and be completely safe to use under all conditions.